问Java wait方法的工作原理

EN

   public class ThreadDemo {
    public static void main(String[] args) throws InterruptedException {
        ThreadImpl thr = new ThreadImpl();
        thr.start();
        Thread.sleep(1000);
        synchronized(thr){
            System.out.println( "MAIN "+thr.hashCode());
            System.out.println("Main -->got the lock");
            thr.wait();
            System.out.println("Main -->Done with waiting");
        }
    }
}

class ThreadImpl extends Thread{
    public synchronized void sayHello(){
        System.out.println("Ssay hello ");
    }
    @Override
    public void run() {
        synchronized(this){
            System.out.println( "METHOD "+this.hashCode());
            System.out.println("METHOD Got the lock ");
            System.out.println("METHOD Going for sleep ");
                for(int i =0;i< 100000;i++);
            try {
                Thread.sleep(2000);
                System.out.println("METHOD Woke up ");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("METHOD Done leaving the thread");
        }
    }
}